The incest monster made a full confession to offences including the murder of his newborn son so he could slip away to a cushy prison cell.

Fritzl, 73, claimed watching his tormented daughter Elisabeth’s harrowing testimony of how he raped her for 24 years made him realise his “sick behaviour”.

But we can reveal the schemer’s real reason for his unexpected change of heart. It was because he faced being turned into a “Fritzl Schnitzel” by the infamous cannibal Robert Ackermann.

He was warned by lawyers he would be sent to Austria’s Goellersdorf asylum where Hannibal Lecter-style killer Ackermann has openly bragged about slicing him up.

Fritzl had read in newspapers how Ackermann, who detests paedophiles and rapists, had vowed to cook him alive – and warders would turn a blind eye.

Ackermann was 19 in 2007 when he ate the brains of Josef Schweiger, 49, after smashing in his skull. Fritzl also realised his defence was pointless after seeing that jurors were so repulsed by 42-year-old Elisabeth’s graphic evidence.

So he altered his plea to dodge being sent to the mental unit and instead will live out his days in a cushy prison.

Fritzl has even chosen the jail he prefers because it offers inmates meditation, tennis, football, darts, singing lessons and cookery classes.

A warder at the prison where Fritzl has been held on remand said: “People jailed for anything involving abusing children always get a hard time from the other inmates.

“They used to bang on his cell and shout: ‘Satan – come out and play.’

“Now they bang on his cell and shout that the cannibal is going to eat him.”

Defence lawyer Rudolf Mayer swung the secret deal to give Fritzl his pick of prisons if he pleaded guilty.

Mayer and prosecution officials agreed that the fiend will serve his time in a single cell. Lawyers announced his dramatic U-turn on Day Three of his trial in the Austrian town of St Poelten yesterday.

He had previously pleaded guilty to incest and the false imprisonment of Elisabeth. But yesterday he admitted murder, slavery, multiple rape and coercion.

It means Fritzl, due to be sentenced today, has almost certainly condemned himself to die in jail.

The murder charge relates to one of the seven children Elisabeth bore him during her 24 years locked in his cellar.

Tragic Michael was born was breathing difficulties and died 48 hours later. Fritzl burned his corpse, but prosecutors say the baby could have been saved had he sought urgent medical help.

He finally apologised yesterday to Elisabeth, who he raped more than 3,000 times in his cellar under the family home in Amstetten.

When the judge asked him why he was changing his plea, Fritzl replied: “My daughter’s videotaped testimony. I’m sorry.”

But, quizzed on why he failed to rush frail Michael to hospital, he told the court: “I don’t know why I did not help. I was hoping he would get through it.”

It emerged last night that Elisabeth was in court to witness her evil dad facing justice. She was freed from the dungeon last April having been drugged and locked away in August 1984.

Psychiatrist Dr Adelheid Kastner told the court that Fritzl had a very serious personality disorder and was “born to rape”.